Thioformamide derivatives of general formula: ##STR3## in which R represents a hydrogen atom or an alkyl radical containing 1 to 4 carbon atoms, Het represents a heterocyclic radical aromatic in nature and Y represents a valency bond or a methylene radical, have been described in European Patent EP 0,097,584.
The presence of two centers of asymmetry leads to 4 stereoisomers which can be optionally separated into 2 racemic pairs which were designated "Form A" (or more polar product) and "Form B" (or less polar product) [the polarity being determined by thin-layer chromatography (TLC)]. These two forms may be resolved.
Among the products of general formula (I), the A form of N-methyl-2-(3-pyridyl)tetrahydrothiopyran-2-carbothioamide 1-oxide consists of a mixture of the transisomers which may be represented in the following manner: ##STR4##
Studies performed on the isomers (II) and (III) have enabled it to be shown that the active form is the isomer (III), the absolute configuration of which is 1R,2R.